Stretching prior to an activity needs to be dynamic (moving) not static (still). Dynamic stretching prepares the body for activity so as to reduce the risk of a tear or pull to our muscles.
Post exercise is when we need to be static stretching, where we hold a stretch for 20-60 seconds depending on how tight our tissue is.
This helps to lengthen the muscle fibres back to their original shape reducing the risk of muscle tightness, inflammation and pain to a bony site or joint.